Semantics.....
Ask the newby what he's doing and he'll say upgrading.
Start with a bone stock classic, buy parts to turn it into an RT Pro (most times this is the eventual end of the process), even if you subtract the cost of the original marker you likely have spent more on the parts than if you had just bought an RT Pro to begin with.
That was the point in case it was missed.
I started with a PF classic with a magic box and a benchy double trigger. Sold a couple of pieces and bought a CF no-rise body, RT-pro with level-10, and i-frame. Somehow that morphed into a cheater pneumag, then a M-90 pneumag, and now it is a Venomous Designs rail and foregrip, ULE, reverse "X-Valve", with both E-90 and M-90.
But I've also taken to building a classic styled setup with some other pieces I've put together.
It's a fun question to ask mag guys "how many different mags can you put together with the pieces you have on hand?" Aside from a few combinations of parts that cannot be put together, you are not limited much in assembling something that is wholly unique to your mood or style of play.
Buy one, play with it, evaluate your setup, and keep plenty of oil and o-rings around.
Stay Classy, AO...BEO: RIP / Topgun Paintball: RIP / Old MCB: RIP
Bah, don't listen to Zondo. You don't need a lot of orings on hand. Fo4 my classic, i put a L10 when they were new, like 2000 or 2001. I have not changed any oring in the gun after countless cases of paint went through it. Other than a few drops of oil(KC Troublefree or the new release of that same oil), that's all you need. Now, i can't say that for the X type valves, but i play with the Mag Whisperer, and he can detect a problem.with a mag at 10 paces. I am spoiled...
A re-build kit will be enough... the only thing I've had to replace are random o-rings. and one foamy for a L10.